Conventionally, there is known a sheet feeding device provided with a feed roller that feeds a sheet to an image forming section of an image forming apparatus, such as an inkjet printer, the feed roller being disposed at a leading end portion of an arm having a base end portion that is rotatably supported by a body of the image forming apparatus.
In the sheet feeding device thus configured, the feed roller is pressed, by an urging force of a spring that presses the arm, on an uppermost sheet of a plurality of sheets that are stacked and accommodated in a sheet feed section that is configured by a sheet feeding cassette whose upper surface is opened.
The feed roller is driven to be rotated while being pressed on the uppermost sheet, thereby to feed the uppermost sheet toward a sloped separation member that is formed at a position downstream to the stacked sheets in a feeding direction. Accordingly, the uppermost sheet is separated from the stacked sheets by the separation member and fed toward the image forming section (refer to JP-A-2005-247521, which is also published as US 2005/0194732 A1).
In the conventional sheet feeding device disclosed in JP-A-2005-247521, the arm is formed by a synthetic resin in a frame shape (or a box shape). The arm is supported by an axis to be rotatable with respect to a drive shaft. The arm is provided with: a driving gear disposed at a position near the base end, the driving gear being configured to rotate integrally with the drive shaft; and a transmission gear train provided at an intermediate portion of the arm in the longitudinal direction, the transmission gear train being configured to transmit power provided from the driving gear to a gear portion that is provided at a side next to the feed roller.
Each of the transmission gears (intermediate gear, or transmission roller) of the transmission gear train is formed with an axis hole at an axis of the rotation. A plurality of spindles, each provided for the respective transmission gears and rotatably supports the respective transmission gears fitted therein, are provided to protrude from an inner surface of one of side plates of the arm.
An elastic member, such as a leaf spring, is provided in the arm to face a side face of each of the transmission gears fitted in the spindles. The transmission gears are pressed into the spindles against an elastic force of the elastic body, to thereby attach the transmission gears in the spindles. According to this configuration, an attachment of the transmission gears is simplified, and the transmission gears once fitted into the spindles are prevented from easily coming off from the spindles.
However, in the configuration disclosed in JP-A-2005-247521, the transmission gears are supported by the spindles protruded from the arm in a cantilevered style. Accordingly, the spindles need to have a considerably large diameter in order to have a rigidity sufficient for withstanding a torque (rotation moment) that acts on the respective spindles when performing a sheet feeding operation.
In a case where the spindle is configured to have the diameter of a large size, a sliding (contact) area where contacts with the axis hole of the transmission gear becomes large, resulting in an increase in frictional force, so that efficiency for driving the transmission gear train is lowered. As a result, a size of the arm needs to be larger, and a drive motor used in the feeding operation is required to have larger torque.
On the other hand, in a case where the transmission gear is configured to have a pair of spindles that protrude from both sides of the transmission gear while supporting the transmission gear by the arm with the pair of spindles, the following configurations will be necessary be employed.
That is, as a first example of the configurations, the arm is configured to be provided with: a first axis hole for supporting one of the pair of spindles is formed on one (first side plate) of side plates of the arm; a second axis hole for supporting the other of the pair of spindles is formed on the other (second side plate) of the side plates that is arranged in parallel with the first side plate; and a means that detachably fix the first and second side plates after the pair of spindles of the transmission gear are inserted into the first and second axis holes. When employing this configuration, the first and the second side plates of the arm need to be formed separable from one another, and the first and second side plates need to be fixed, thereby raising a manufacturing cost.
As a second example of configurations, the first and the second side plates of the arm are arranged in parallel with one another to have a predetermined distance therebetween (the distance is configured to be substantially equal to a width of the transmission gear). The first and second axis holes are formed on the first and second side plates, and an axis hole is formed on the transmission gear. After a spindle is inserted into the first and second axis holes and the axis hole that is formed on the transmission gear, a stopper member is attached for preventing the spindle member from coming off. When employing this configuration, a number of components is increased, and the insertion of the spindle member into the three axis holes becomes troublesome, thereby raising a manufacturing cost required for assembling the arm.